1. Field of the Invention
The present invention relates to antenna architectures and methods on re-configurable antennas via feed re-positioning for various optimized radiation contours, including beam forming (or shaping) and/or null steering on contoured beams, spot beams, and orthogonal beams. The feed re-positioning techniques can also be used in radiation pattern optimization processing during antenna design phases for fixed beams.
2. Description of Related Art
The present invention relates to antenna architectures and methods on re-configurable antennas for all wireless RF communications via feed re-positioning for various optimized radiation contours. The feed re-positioning techniques can also be used in optimizing radiation pattern processing during antenna design phases for fixed beams.
We focus applications on satellite communications on this disclosure. However, similar designs based on same principles are applicable for other RF systems including radars, radiometers, terrestrial point-to-point and point-to-multiple points wireless communications, airborne GPS antennas; just to name a few.
Satellite Ground Terminals
A satellite ground terminal is designed to maintain RF transmission links between itself and a designated satellite while minimizing interference to and from other nearby satellites. In order to maximize orbital space utility, satellites covering the same areas with the same spectrum are kept relatively far from one another—at least 2° apart, enabling satellite operators to reuse the same spectrum independently for the same coverage.
A satellite ground terminal usually comes with a beam forming design constraint that enables the terminal to point in a desired satellite direction with a certain gain. Beam forming is a concept of using interference to change directionality of radio waves to: focus a signal in a desired direction, boost signal strength, and to reduce signal emissions in undesired directions. The corresponding beam-widths from specified antenna apertures are smaller than the spacing among adjacent satellites covering the same areas with the same frequency bands. However, as the number of satellites in the Earth's geo-synchronous orbit increases due to rising demand, the need rises for additional constraints on ground terminals for both transmit and receive functions-beam nulling.
Beam nulling [1, 2, 3, 4] is another feature of beam forming process that manipulates the multiple array antenna elements of a satellite ground terminal in such a way that the spatial combining effects due to propagation path differential minimize the terminal radiation in certain directions within a transmit frequency band. At the same time, beam nulling can also significantly reduce the ground terminal receiving sensitivity in the same (or other) directions within the receiving frequency band, thus helping to resolve the issue of interference from other satellites.
Normally, geostationary orbit (GEO) satellites operating within the same radio wave spectrum or frequencies are placed in orbit 2° apart. This is to reduce interference between satellites for the ground operator, as well as maximizing available satellite resources. If the two adjacent satellites are closely spaced—less than 2°—the proposed ground terminals will enable both operators to reuse the available spectrums independently for the same coverage, maximizing the utility of the available bandwidth. The signal isolations between the two satellite systems are achieved via spatial isolation alone, not by frequency or time diversities. With more than two satellites in close proximity, the proposed terminals have the capability of forming a beam peak in their respective satellite's direction and forming close-in nulls in the directions of the nearby interfering satellites. The angular discriminations on ground terminals are achieved via array element placement.
Satellite Antennas
In a similar fashion to the mobile terminal antenna applications, the mechanical adjustment techniques can be applied very cost effectively to satellite on-board antenna designs. This can give communications satellites occasional coverage re-shaping capability without the need for electronic signal processing.
Current inventions are designed for satellite antenna architectures with multiple feeds, including direct radiating arrays, magnified phased arrays, and defocused multiple-beam antennas (MBA's). On the other hand, the beam shaping or reconfigurable mechanisms are via re-positioning of array feeds of an antenna. The repositioning includes (1) linear translations of feed elements in a, y, and z directions, (2) feed element rotations through the element center and parallel to x, y, and z axes, and (3) combinations of (1) and (2).
In addition, commercial satellite services sometimes call for contour beam shaping, which utilizes a specially shaped reflector surface to cover desired coverage areas [5, 6]. There are techniques to have one common shaped reflector with multiple switching feeds for a few “re-configurable” coverage areas [7, 8, 9]. However, these coverage areas must be determined during the design phase as the reflector shape must be manufactured under the constraints of known potential coverage areas. Each area is by a designated feed or a combination of a set of designated feeds. Variable area coverage is achieved via switching to different feeds or different sets of feeds.
The design process may be based on computer simulations or actual range measurements via performance optimizations, and the associated performance constraints will be set for single beam or multiple beams, and for single frequency band or multiple frequency bands.
The optimization process may also be tested and utilized with antenna farm integration in mind, minimizing mutual interferences and cross polarizations among various reflectors antennas for both receive (Rx) and transmit (Tx) functions by repositioning of reflectors antennas or auxiliary feeds. Then, the feeds may be configured as directed radiation elements or defocused feeds to reflectors.